Oh, sorry...
as to your actual question: yes, like pretty much all smartphones, the Samsung Galaxy S5 CAN deal with 2 calls at a time. BUT: it depends on your network if it is possible for YOUR Galaxy S5.

Also: I have seen a number of forum threads that discuss issues with the Galaxy S5 - apparently a number of users experience a problem where ending call #1 will also cut off call #2... But that could be a network issue? (though - Samsung are no strangers to bizarre bugs. Buy a Galaxy Camera or an Ace to see the best ones)